Drop folder api permissions


We have been trying to add some custom metadata to our drop folder items and are getting this error:

customDataItems failed: The access to service [metadata_metadata->list] is forbidden

After checking checking the following tables: permission, permission_item and permission_to_permission_item, I noticed that some rows are missing compared to our dev server where everything works OK.

Which permissions should I add or are needed to the drop folder processes in order to work properly ?

Thank you in advance for any help,